1. Field of the Invention
This invention relates to the field of semiconductor devices. More particularly, the invention relates to a method and apparatus for allowing phase conflicts between phase shifting regions in a phase shifting mask to be used in optical lithography processes for manufacturing integrated circuit devices.
2. Description of the Related Art
Semiconductor devices continue to be produced at reduced sizes as optical lithography processes have evolved. Techniques such as phase shifting have been developed to assist in the production of subwavelength features on the integrated circuits (IC) using optical lithography processes. Subwavelength features are features that are smaller than the wavelength of light used to create circuit patterns in the silicon. More generally, phase shifting can be used to create features smaller than a minimum realizable dimension for the given process.
Through the use of phase shifting masks, such subwavelength features can be efficiently produced. (Note, that the term xe2x80x9cmaskxe2x80x9d as used in this specification is meant to include the term xe2x80x9creticle.xe2x80x9d) One approach to producing a phase shifting mask (PSM) is to use destructive light interference caused by placing two, out of phase, light transmissive areas in close proximity in order to create an unexposed region on a photoresist layer of an IC. If that unexposed area is then protected from exposure when a binary mask is used to expose the remaining field (thus causing definition of the remaining structure), the resultant IC will include subwavelength features created by the PSM.
One approach to preparing an IC for production using PSMs is for one or more features of the IC to be identified for production using PSMs. For example, a designer might identify one or more particular features for production using the PSM, e.g. to define the identified gates (or other features) at subwavelength sizes.
A portion of a design layout 100 for a layer in an IC is shown in FIG. 1. Several distinct portions of the design layout are identified, particularly a gate 102 and a gate 104. In this example, both the gate 102 and the gate 104 are identified as xe2x80x9ccriticalxe2x80x9d, e.g. to be produced using a phase shifting mask.
A phase shifting mask 200 for defining the gate 102 and the gate 104 is shown in FIG. 2. The phase shifting mask 200 includes three light transmissive regions: a light transmissive region 202, a light transmissive region 204, and a light transmissive region 206. Light transmissive region 202 and light transmission region 204 are out of phase with one another, e.g. light through one is at phase 0 and the light through the other at phase xcfx80. Similarly, light transmissive region 204 and light transmissive region 206 are out of phase with one another, continuing the example if the light transmissive region 204 is at phase xcfx80, then the light transmissive region 206 would be at phase 0. These light transmissive regions are sometimes referred to both individually and collectively as phase shifters (the meaning will be apparent from usage). Additionally, the light transmissive regions are sometimes referred to as phase shifting areas. Note that between the light transmissive regions there is some protect (usually chrome) that assists in the definition of feature size and improves mask manufacturability.
FIG. 2 also illustrates that it is generally preferable to make the phase shifters (e.g. the light transmissive region 202, the light transmissive region 204, and the light transmissive region 206) relatively wide compared to the wavelength of the light (xcex). For example, some phase shifting processes attempt to make the total width of the phase shifters and the protective area between them approximately 3xcex. In this example, due to the proximity of the gates, instead of having two separate light transmissive regions between the gate 102 and the gate 104, a single light transmissive region, the light transmissive region 204 is used.
If two light transmissive regions were used for the light transmissive region 204, they would be assigned the same phase to prevent definition of an artifact on the IC. Similarly, if the light transmissive region 202 had to be of phase xcfx80 and the light transmissive region 206 had to be of phase 0 (for example because of surrounding phase shifters, etc.), then a phase assignment problem would arise with respect to assigning phase to the light transmissive region 204. For example, if the phase assigned is 0 then, the gate 104 would not be successfully defined. Further splitting the light transmissive region 204 into two parts would produce an undesirable artifact on the IC.
Accordingly, what is needed is a method and apparatus for allowing phase assignment conflicts between phase shifting regions in a phase shifting mask. Additionally, both a phase shifting mask with phase assignment conflicts and a complimentary binary mask that can produce ICs with subwavelength structures is desired.
Frequently, phase shifting masks use chrome (or other protective materials) between edges of two phase shifters to improve mask manufacturability and critical dimension control. However, the requirement of a chrome (or other protective) edge on the phase shifting mask may make definition of certain densely packed features extremely difficult.
Accordingly, what is needed is a method and apparatus for allowing chromeless (or, more generally, protectless) phase transitions in a phase shifting mask. Additionally, both a phase shifting mask with chromeless phase transitions and a complimentary binary mask that can produce ICs with subwavelength structures is desired.
Phase shifting layouts and masks with phase conflicts are described. The phase shifting layout defines light transmissive regions for use in defining selected features in a layer of material of an integrated circuit (IC). The selected features are sometimes referred to as critical features. The selected features are simply those features within a given layout, or portion of a layout, that a designer has specified would be desirable to produce using phase shifting. The selected features can then be produced at subwavelength sizes and can be more densely packed.
If the selected features are in relatively close proximity to one another, it may be difficult to assign phase to each of the light transmissive regions in the phase shifting layout. That is because the light transmissive regions on opposite sides of a given feature must be of opposite phase. Some IC layouts may have the selected features in an arrangement that makes it impossible to assign phase to the light transmissive regions so that the selected features can all be defined.
By adding a phase transition (and optionally control chrome) to subdivide one or more the light transmissive regions, it may then be possible to assign phase to all of the light transmissive regions so that all of the selected features are defined by the phase shifting mask. However, the added phase transition introduces a (intentional) conflict that if used, without correction, would lead to the definition of an artifact, or simply a structure, in the layer of material. This phase conflict is sometimes referred to as a false phase conflict since allowing it the layout data does not prevent the resultant mask from being used to successfully define the selected features.
A corresponding mask for use in conjunction with the phase shifting layout that includes the false conflict can also be defined. In one embodiment, a binary trim mask is used. The corresponding mask is characterized by the fact that when used in conjunction with the phase shifting mask, the artifact created by the false phase conflict will not be produced in the layer of material. If a binary trim mask is used, this can be accomplished by ensuring that there is an absence of protect (usually chrome) in the area of the trim mask corresponding to the location of the false phase conflict on the phase shifting mask.